Birds

A “binge and fast” approach to life – storing up body fat at some times, then living off reserves during migration, courtship and breeding – means that birds are particularly susceptible to pollution.

In the 1960s, it became apparent that DDE, a breakdown product of the pesticide DDT, caused eggshell thinning. Because DDE is persistent and accumulates in fat, birds at the top of the food chain, including birds of prey and seabirds, were particularly affected, several being brought close to extinction. Effects linked to DDT include skewed sex ratios and female-female pairing in gull populations. Fish eating birds are particularly exposed to chemical contaminants. However, with the banning of DDT, populations have virtually returned to normal in some species such as the Baltic guillemot. But where DDE contamination remains significant eggshell thinning continues to be a problem, other populations are still at risk – for example, the peregrine falcon in Canada and Russia, and the coastal peregrine falcon in Britain.

Other, current-use chemicals, like flame retardants also lead to contamination of birds eggs.In birds, pollutant related effects include: abnormal production of the egg yolk protein in male birds which is normally produced in females; deformities of the reproductive tract; embryonic mortality; reduced reproductive success including egg-shell thinning; and poor parenting behavior.

CHEM Trust report Effects of Pollutants on the Reproductive Health of Male Vertebrate Wildlife – Males Under Threat, by Gwynne Lyons shows that male fish, amphibians, reptiles, birds and mammals have been harmed by chemicals in the environment. Widespread feminisation of male vertebrate wildlife is highlighted. These findings add to mounting worries about the role of hormone-disrupting or so-called ‘gender-bending’ chemicals in the environment, and the implications for human health.